The present invention relates to ceramic body and a glass composition having a low softening temperature suitable for bonding and filling ceramic constituent parts thereof, and particularly suitable for bonding and filling ferrite constituent parts used for highly efficient magnetic heads.
A glass composition used for binding and filling the ceramic constituents, particularly ferrite constituents, is required to have a low softening temperature, which is one of parameters for accessing a working temperature of the glass, so as to minimize adverse thermal influence on the ceramic constituents and further on materials supported on the ceramic constituents, for example an amorphous alloy, during the bonding and filling operation.
The glass is further required to have a little smaller thermal expansion coefficient than that of the ceramic constituents to be bonded and filled so as to minimize generation of cracks in the bonding and filling glass, which reduces the adhesive strength of the glass.
The thermal expansion coefficient of the ferrite constituents used for the magnetic heads is 90-140.times.10.sup.-7 /.degree.C. in the range from room temperature to 300.degree. C.
One of conventional low softening temperature glasses is a glass composition including primarily lead oxide PbO such as PbO-B.sub.2 O.sub.3 system, PbO-B.sub.2 O.sub.3 -ZnO system, PbO-B.sub.2 O.sub.3 -SiO.sub.2 system and variations of PbO-B.sub.2 O.sub.3 -SiO.sub.2 system.
Generally, the lower a softening temperature of a glass composition is, the larger a thermal expansion coefficient of the glass is, which is naturally true with the above PbO glass, in that, when an amount of PbO in the glass increases, the softening temperature thereof lowers, however adversely the thermal expansion coefficient increases.
Further the PbO glass corrodes the ferrite constituents at the boundary with the PbO glass so that a magnetic property of the ferrite is reduced.
Still further the PbO glass has a low abrasive resistance which is not desirable as a bonding and filling material for the ferrite constituents of the magnetic heads.
Another conventional low softening temperature glass than the PbO glass is a glass composition including Vanadium pentoxide V.sub.2 O.sub.5 as the main component which has a lower transition temperature, a lower yield temperature which are also parameters for accessing a working temperature of the glass and further a smaller thermal expansion coefficient than those of the low softening temperature glass including PbO as the main component. However the V.sub.2 O.sub.5 glass loses the fluidity because of an excess crystallization during reheating of the glass so that a higher working temperature is necessitated for a sufficient bonding and filling. The crystallization of the V.sub.2 O.sub.5 glass during the reheating is to be limited by decreasing the amount of V.sub.2 O.sub.5 in the glass, which however raises the transition temperature and the yield temperature of the V.sub.2 O.sub.5 glass.
Japanese Patent Application Laid Open Print No. 53-82826 (Published on July 21, 1978) discloses one example of a low softening temperature glass including V.sub.2 O.sub.5, in that, glass of 7.5-14 wt%Na.sub.2 O-20-50 wt%ZnO-0-35 wt%B.sub.2 O.sub.3 -20-60 wt%P.sub.2 O.sub.5 -3-15 wt%V.sub.2 O.sub.5 system used for bake-painting metal plates with a comparatively low heat resistance such as aluminium plates and thin iron plates and for sealing. However the disclosed glass has a relatively large thermal expansion coefficient of 91-142.times.10.sup.-7 /.degree.C. which is improper for applying to the ferrite constituents and further has a relatively high softening temperature of about 500.degree. C.
Japanese Patent Application Laid Open Print No. 58-74539 (Published on May 6, 1983) discloses another example of a low softening temperature glass including V.sub.2 O.sub.5, in that, glass of 15-35 wt%B.sub.2 O.sub.3 -7-22 wt%ZnO-0-5 wt%V.sub.2 O.sub.5 -19-39 wt%Bi.sub.2 O.sub.3 -19-39 wt%Tl.sub.2 O system used for bonding and filling ferrite constituents for magnetic heads. The disclosed glass does not corrodes the ferrite constituents, has a smaller thermal expansion coefficient of 80-90.times.10.sup.-7 /.degree.C. than that of the ferrite, however has a high softening temperature of 560.degree.-600.degree. C. which increases a working temperature of the glass.